diff --git a/htdocs/tz.php b/htdocs/tz.php
index 8cbb4f28..3ec56171 100644
--- a/htdocs/tz.php
+++ b/htdocs/tz.php
@@ -14,7 +14,7 @@ $session = new PublicSession();
 
 param_to_global('action','{[a-z_-]+}');
 param_to_global('format','{[a-z]+/[a-zA-Z0-9.+_-]+}');
-param_to_global('changesince');
+param_to_global('changedsince','{.*}','changesince');
 param_to_global('start');
 param_to_global('end');
 param_to_global('lang');